Date: Sun, 24 Feb 2019 14:07:33 +1100 From: Peter Jeremy <peter@rulingia.com> To: freebsd-arm@freebsd.org Subject: Fixing the missing "cpu" devclass on RPi Message-ID: <20190224030733.GA11137@server.rulingia.com>
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On the RPi, the "cpu" devclass is created by dev/ofw/ofw_cpu.c and depends
on the presence of a "cpus" block in the FDT. This exists in the FreeBSD
trees (eg bcm2835-rpi-b-plus.dtb) but not in the Linux FDT populated by the
latest firmware. This means that (eg) bcm2835_cpufreq never gets probed[1].
Injecting "cpus" via a fdt overlay was suggested but I can't get that to
work. I have rpi-cpus.dtso as follows:
=3D=3D=3D=3D=3D
/dts-v1/;
/plugin/;
/ {
compatible =3D "brcm,bcm2835";
};
&{/} {
cpus {
cpu@0 {
compatible =3D "arm,1176jzf-s";
device_type =3D "cpu";
};
};
};
=3D=3D=3D=3D=3D
When I compile it and de-compile it, the result looks sane:
=3D=3D=3D=3D
$ dtc -I dtb -O dts rpi-cpus.dtbo
/dts-v1/;
/ {
compatible =3D "brcm,bcm2835";
fragment@0 {
target-path =3D "/";
__overlay__ {
cpus {
cpu@0 {
compatible =3D "arm,1176jzf-s";
device_type =3D "cpu";
};
};
};
};
__symbols__ {
};
};
=3D=3D=3D=3D
I've added rpi-cpus.dtbo to fdt_overlays in loader.conf and the boot
messages report that it's being loaded but the "cpus" section is still
missing from hw.fdt
I presume I've got something wrong in my dtso but I'm not sure what -
I haven't found a great deal of documentation on writing overlays and
the above looks correct according to what I've found.
[1] There's a separate bug in bcm2835_cpufreq.c so it'll never attach,
but that's just a matter of fixing the compatible list.
--=20
Peter Jeremy
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